<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>has demo</title>
    <style>
        .full {
            border: 1px solid red;
        }
    </style>
    <script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>

<ul class="full"><li>Does the UL contain an LI?</li><li>Yes</li></ul>

<script>
    $( "ul" ).append( "<li>" +
            ( $( "ul" ).has( "li" ).length ? "Yes" : "No" ) +
            "</li>" );
    $( "ul" ).has( "li" ).addClass( "full" );
</script>

</body>
</html>